Apparatus and methods for water treatment

ABSTRACT

An apparatus and method for treatment of water borne oxidized contaminants, using hydrogen as an electron donor for denitrification and reduction of other oxidized contaminants. Preliminary results reported here show that a biofilm of autotrophic denitrifiers accumulates rapidly in the wastewater setting, the MBfR can drive NO 3   −  concentrations below 1 mgN/L, and the H 2  pressure controls the NO 3   −  flux.

This application is a continuation of and claims priority benefit fromapplication Ser. No. 10/876,745 filed on Jun. 25, 2004, now U.S. Pat.No. 7,338,597 which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Wastewater denitrification protects water resources from nutrientenrichment and accelerated eutrophication. Problems associated witheutrophication include excessive algae growth, turbidity, foul taste andodors, accelerated sedimentation, pathogen growth and hypoxia. Suchissues are exacerbated when the wastewater is discharged into a lake,reservoir, estuary or delta, but most pronounced when the discharge is alarge portion of a stream or river flow. As a result, the regulation ofnitrogenous wastes is bound to become more stringent in the near future.Reliable and cost-effective means to reduce nitrogen concentrations toincreasingly lower levels are needed. In response, biologicaldenitrification—bacterial conversion of oxidized nitrogen contaminantsto harmless nitrogen gas—has received some attention in the art.

One such approach is described in U.S. Pat. No. 6,307,262, the entiretyof which is incorporated herein by reference. A hollow-fiber membranebiofilm reactor (MBfR) introduces hydrogen gas as an electron donor toinduce growth of hydrogen-oxidizing bacteria on the membrane's surface.Such bacteria, in turn, reduce oxidized nitrogen contaminants tonitrogen gas. Hydrogen is an efficient and cost-effective reagent thatavoids the toxicity and material-handling problems associated withorganic electron donors of the prior art. The MBfR alleviates many priorconcerns associated with hydrogen, including low solubility and highflammability. Hydrogen diffuses from lumen of the fibers toward theaqueous medium, promoting biofilm growth. Use of a hydrophobicconstruction material permits the membrane pores to remain dry. Nohydrogen bubbles are formed, and little or no hydrogen is carried outbut through the treated water, minimizing additional oxygen demand.

Even so, the MBfR technology embodied in the '262 patent does not alwaysprovide a complete solution to wastewater treatment. For instance, thehollow fiber membranes are confined to a tubular configuration andrequire, by design, movement of the aqueous contaminants along thelongitudinal fiber axes. One or more water pumps are needed forrecirculation and continuous reaction. The tubular configuration doesnot lend itself to existing wastewater treatment basins, and the fiberdensity impedes movement of solids through and out of the reactor.

One of the emerging challenges for wastewater treatment is achievingvery low effluent concentrations of total nitrogen (TN) and totalphosphorus (TP). Increasingly severe problems with eutrophication andhypoxia in lakes, reservoirs, estuaries, and the near-shore ocean areforcing environmental regulators to impose more stringent effluentrequirements on TN and TP. For example, an effluent standard for TNcould be 1 mgN/L when the discharge is to a sensitive water body; it ispossible that a receiving-water standard of 0.12 mgN/L could be appliedif the wastewater were the dominant water input.

Existing wastewater-treatment technology is capable of taking effluentTN down to the range of 10-15 mg//L, but it is neither reliable norcost-effective for achieving ≦1 mgN/L. A key for taking TN down to the1-mg/L level is stable denitrification to drive NO₃ ⁻—N to a few tenthsof a mg/L. Stable nitrification can drive NH₄ ⁺—N to a few tenths of amg/L, and filtration can bring organic N to almost zero. If solubleorganic nitrogen can be held to a few tenths of a mg/L, total N could bereduced to about 1 mg/L: e.g., 0.2 mg/L NH₄ ⁺—N and 0.3 mg/L NO₃ ⁻—Ntotaling 0.5 mg/L soluble organic N.

Pre-denitrification can utilize influent biological oxygen demand (BOD)to fuel denitrification, but realistic constraints on the mixed-liquorrecycle rate limit it to about 75% N removal, which leaves about 10 mg/LTN in the effluent when the influent is 40 mgN/L. Furthermore, a highinfluent TKN:BOD ratio can foil the pre-denitrification strategy as ameans for total N removal. Return of digester supernatants is a commonsituation leading to a high influent TKN:BOD ratio.

Tertiary denitrification using an organic electron donor, such asmethanol or acetate, could, in principle, drive effluent NO₃ ⁻ to a fewtenths of a mgN/L. However, the dosing of the organic donor cannot becontrolled well enough to ensure full NO₃ ⁻ removal without massivedonor overdosing that increases effluent BOD and wastes money. Inaddition, tertiary denitrification using an organic donor significantlyincreases excess sludge production and often involves special chemicalhandling. For example, methanol (CH₃OH) is popular for its relativelylow cost, but methanol is a dangerous chemical that is toxic to humans,is regulated, has very difficult handling properties, and is oxidizedonly by specialized methanotrophs.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional illustration of a membranecomponent, in accordance with this invention.

FIG. 2A is a schematic illustration of an apparatus for denitrificationof an aqueous system, in accordance with this invention and as can beused in conjunction with a membrane component of the type illustrated inFIG. 1.

FIG. 2B is a top view of the apparatus of FIG. 2A.

FIG. 2C is a top view of an alternate water treatment apparatus, inaccordance with this invention.

FIG. 3 provides a schematic representation illustrating removal ofoxidized contaminants, regardless of apparatus or membrane componentconfiguration, in accordance with this invention.

FIG. 4 illustrates schematically use of the present invention fortertiary denitrification, in conjunction with a pre-denitrificationprocess, in accordance with this invention.

FIG. 5 illustrates the integration of the methods and apparatus of thisinvention into a pre-denitrification system to augment removal ofoxidized nitrogen contaminants.

SUMMARY OF THE INVENTION

In light of the foregoing, it is an object of the present invention toprovide an apparatus and one or more methods for groundwater, drinkingwater, and/or wastewater treatment to remove nitrate and other oxidizedcontaminants, thereby overcoming various deficiencies and shortcomingsof the prior art, including those outlined above. It will be understoodby those skilled in the art that one or more aspects of this inventioncan meet certain objectives, while one or more other aspects can meetcertain other objectives. Each objective may not apply equally, in allits respects, to every aspect of this invention. As such, the followingobjects can be viewed in the alternative with respect to any one aspectof this invention.

It is an object of the present invention to provide an apparatus for usewith existing treatment facilities and configurations, therebyeliminating the need for recirculation pumps of the prior art. As arelated objective, the methods and apparatus of this invention canpromote movement of aqueous contaminants without restriction to thelongitudinal aspect of any fiber membrane component.

It is another object of the present invention to provide an apparatusfor wastewater treatment, with variable membrane and/or fiber density,to facilitate movement of solid particles throughout without impedingcirculation or discharge.

It is another object of the present invention to provide a method and/orapparatus used in conjunction therewith for enhanced total nitrogenremoval, as can be evidenced by effluent concentrations less than about1 mg/L.

It is also an object of the present invention to provide the wastewaterdenitrification methodology useful in conjunction with or as an adjunctto existing pre-denitrification techniques—whether in the context ofwastewater treatment or removal of oxidized contaminants from groundand/or drinking water sources.

Other objects, features, benefits, and advantages of the presentinvention will be apparent from this summary and its descriptions ofvarious preferred embodiments, and will be readily apparent to thoseskilled in the art having knowledge of oxidized contaminants andassociated water treatment techniques. Such objects, features, benefitsand advantages will be apparent from the above as taken into conjunctionwith the accompanying examples, data, figures, and all reasonableinferences to be drawn therefrom, alone or with consideration of thereferences incorporated herein.

In part, the present invention comprises an apparatus fordenitrification of an aqueous system. Such an apparatus comprises (1) ahydrogen source; (2) a plurality of membrane components, each membranecomponent further comprising a passage for hydrogen gas, and eachmembrane component positioned at a point proximate to the hydrogensource and at a point distal to the hydrogen source; and (3) an inletcomponent coupling the hydrogen source and the membrane components.Alternatively, the membrane components of such an apparatus arepositionally configured to define intercomponent spaces for mixed watermovement therethrough. In certain embodiments thereof, theintercomponent spaces are dimensioned sufficient for transverse movementof water thereabout. Each such apparatus embodiment is distinguishablefrom and can be practiced separate and apart from other embodiments ofapparatus or methods described herein.

Regardless, membrane components can be arranged and configured toprovide fibers and/or sheets. In certain embodiments, the components aresealed at an end opposite the inlet component. In certain otherembodiments, the membrane components are coupled to more than onehydrogen source and a corresponding number of inlet components. As wouldbe understood by those skilled in the art, a manifold inlet componentcan couple a plurality of membrane components to a particular hydrogensource.

In certain embodiments, whether provided in fiber, sheet, and/or analternate arrangement, the membrane component can be positioned in a rowconfiguration. Alternatively, fiber membrane components can bepositioned in a configuration of rows and columns. With respect to thelatter, one or more grid support components can be used to position thefibers at points with respect to one or more hydrogen sources.

As discussed more fully below, each membrane component comprises asubstantially non-porous member and/or subcomponent functionallyconfigured to provide hydrogen gas substantially without bubbleformation. In certain embodiments especially useful with this invention,such a membrane component can comprise inner and outer layers having afirst density and a layer therebetween having a second density laterthan the first density. Components found especially useful have asubstantially non-porous layer between the aforementioned inner andouter layers.

Likewise, as described below, the membrane components can havehydrogen-oxidizing bacteria thereon, under conditions fordenitrification or reduction of other oxidized contaminants.Accordingly, an apparatus of this invention can further comprise acontainer found in water treatment facilities. In particular, such anapparatus can be used in conjunction with an activated sludge tank ofthe sort used for wastewater treatment.

In part, the present invention also includes a method for watertreatment. Such a method comprises (1) providing an aqueous systemcomprising hydrogen-oxidizing bacteria, a water borne oxidizedcontaminant, a hydrogen source, and an apparatus of the sort describedabove comprising a plurality of membrane components; (2) contacting thesystem with gaseous hydrogen; and (3) reducing the contaminant. Oxidizedcontaminants treated with the present methodology include but are notlimited to nitrate, nitrite, perchlorate, chlorate, chlorite, selenate,selenite, arsenate, bromate, chromate, chlorinated hydrocarbonsincluding chloroform, dichloromethane, dichloroethane, trichloroethane,tetrachloroethane, trichloroethene, and combinations of suchcontaminants. Whether alone or in combination with another, such anoxidized contaminant optimally has a system concentration sufficient forsupporting accumulation of hydrogen-oxidizing bacteria.

As discussed above, the membrane components can be arranged as one ormore fibers and/or sheets, with each such component coupled to one ormore hydrogen sources. Positional configuration of such components candefine intercomponent spaces for movement of water therethrough. Withoutlimitation and as a departure from the prior art, such intercomponentspacing allows movement of water-borne oxidized contaminants transverseto the membrane components, as found especially useful in the treatmentof wastewater and other aqueous systems comprising solid particles.While wastewater and the like could compositionally comprise organicelectron donors, it will be appreciated by those skilled in the art thatthe methods of this invention can be effected with hydrogen gas, alone,without need for addition of another electron donor source.

Accordingly, the present invention also includes a method of using amembrane configuration for denitrification of wastewater. Such a methodcomprises (1) providing an apparatus of the sort described herein,comprising a hydrogen source and a plurality of membrane componentshaving hydrogen-oxidizing bacteria thereon; (2) introducing to theapparatus wastewater comprising an oxidized nitrogen contaminant; and(3) supplying the apparatus with gaseous hydrogen. Regardless ofmembrane embodiment, whether fiber, sheet or alternate arrangement, thewastewater can be moved by mixing or circulation transverse to themembrane components.

Optimal denitrification proceeds with oxidized nitrogen contaminant(e.g., nitrate or nitrite) wastewater concentration(s) sufficient tosupport accumulation of hydrogen-oxidizing bacteria on the membranecomponents. As such, hydrogen gases are preferably suppliedsubstantially without bubble formation and can be achieved with amembrane component comprising a substantially non-porous member.

The oxidized nitrogen contaminant can comprise an aerobic treatmentproduct of a reduced nitrogen contaminant in wastewater. That is, areduced nitrogen contaminant (e.g., ammonium ion, etc.) can be oxidizedunder aerobic conditions, with subsequent reduction of the correspondingoxidation product via hydrogen-oxidizing bacteria. Accordingly, thepresent methodology can be utilized as part of a tertiary treatmentprocess, post-pre-denitrification, or as integrated in apre-denitrification system to enhance performance. Regardless,denitrification as described herein can reduce total oxidized nitrogenconcentration to a level less than about 1 mg/L.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Hydrogen is an ideal electron donor for bioreactors reducing oxidizedanions because (1) it is less expensive, per electron equivalent, thanorganic donors, such as acetate or methanol; (2) it is non-toxic,increasing public acceptance for its use for water treatment; (3) it issparsely soluble, so it is not possible to “overdose” the system andcause re-growth; and (4) it can be generated on-site. The historicdisadvantage is that hydrogen is difficult to deliver without sparging,a wasteful and potentially dangerous process. However, a hydrogen-basedbioreactor, such as a membrane biofilm reactor (MBfR) of the typedescribed herein, can deliver hydrogen safely and efficiently withoutsparging.

Pressurized hydrogen is supplied to the component interior and diffusesto a biofilm growing on the membrane surface. The biofilm consumeshydrogen as it reduces oxidized contaminants present in the water.Schematically illustrated in FIG. 1, membrane component 10 can comprisenon-porous layer structures 12 positioned between outer and innermicroporous layer structures 14 a and 14 b, respectively. Passage 16, asdefined by such a configuration, provides hydrogen gas for diffusionthrough membrane component 10 and consumption by biofilm 18.

The membrane illustrated in FIG. 1 represents but one configurationuseful in conjunction with the present invention. Various other membranearrangements and configurations can be utilized, limited only by theirability to provide hydrogen gas to a system at a rate and concentrationwith consideration of the solubility of hydrogen in water and the riskof explosion. Generally, good results and economy are achieved with amembrane that can reduce, minimize, or eliminate bubble formation. Forinstance, a hollow membrane constructed of a dense, non-porousmaterial—whether or not wholly or in part provided with one or moremicroporous components (e.g., adjacent to or therebetween)—can be usedwith good effect. For instance, membrane component 10 can be constructedfrom two non-porous layer structures 12 absent outer microporousstructure(s) 14 a, absent microporous structure(s) 14 b, or absent bothmicrostructure(s) 14 a and 14 b. Likewise, a single non-porous structure12, with or without any combination of microporous structures 14 a and14 b, can be used effectively with passage 16 (e.g., attached conduit,duct, etc.) providing adequate connection with a hydrogen source, suchconnection sufficient for accumulation of hydrogen-oxidizing bacteria onmembrane component 10. Various other arrangements or configurations canbe employed with the understanding that increased bubble formationincreases risk of explosion, lowers system economy, and tends to disruptbiofilm formation.

Likewise, the apparatus of this invention is not limited to any onearrangement or configuration. Variations of biofilm reactor 20 are shownin FIGS. 2A-C. With non-limiting reference to FIG. 2A, apparatus 20 canbe situated within tank 22 containing an aqueous medium of oxidizedcontaminants. One or more support grids 24 positionally configure fibermembrane components 26 and can be, as shown, suspended fromtank/container closure 28. Fiber membrane components 26 are coupled to ahydrogen source via inlet 30 and extend to terminus 32. Influent port 34and effluent port 36 can be used to regulate treatment rate and volume.Mixing/stirring mechanism 38 can comprise a paddle or similar suchcomponent useful in treatment of wastewater, to facilitate movement ofwater borne contaminants about the membrane components.

Hydrogen gas is directed inside fiber membrane components 26 from thehydrogen source. With sealed fiber ends, the hydrogen gas is containedunder a controlled pressure within individual fibers. The gas candiffuse through a non-porous layer structure of the sort describedabove, for metabolic interaction with an accumulated biofilm and thesubject oxidized contaminant(s). Such conditions induce a high drivingforce for gas dissolution without bubble formation. Other componentsuseful with apparatus 20 can vary as any suitable system known in theart may be used for water delivery to and removal from container 22.Likewise, those skilled in the art will appreciate that such anapparatus can further comprise components for pH control andintroduction of other water treatment reagents.

Hollow fibers of the sort useful in the apparatus of FIGS. 2A-B aremanufactured by Mitsubishi Rayon (Model MHF 200TL) and are available asa composite. The wall of the particular fiber was made up of twodifferent materials. The outer and inner layers of the fiber wall werecomposed of microporous polyethylene. Between the two layers was a1-micron thick layer of non-porous polyurethane. This non-porous layerallowed the creation of a high driving force for gas dissolution withoutpremature bubble formation, the desirability of which is as previouslymentioned. The hollow fibers were sealed on one end and open to thepressurized hydrogen supply on the other end. With reference to FIG. 2B,rows and columns of such fiber membrane components 26 can be arranged ingrid support component 24. An alternate membrane arrangement is shownschematically in FIG. 2C, where such components are provided aspositionally configured sheets 40. As mentioned above, however, inconjunction with FIG. 1, other membrane component constructions and/orconfigurations can be used without regard to number, form, scale ordimension.

As discussed elsewhere herein, MBfRs of the prior art are effective forremoving oxidized contaminants from ground and drinking water, but lesssuited for a wastewater setting. Wastewater contains a large amount ofsolids, which could lead to fouling in an enclosed-tube configuration,such as that described in the '262 patent. An MBfR used in conjunctionwith a container or basin provides greater membrane choice and/orseparation, would allow for mixing with less energy, and would allowgreater flexibility for cleaning and maintenance. Additionally, thepresent invention now provides for retrofitting an existing activatedsludge tank.

Accordingly, an MBfR apparatus of this invention, useful in conjunctionwith an activated sludge basin, was developed for treating wastewater.One embodiment of a reactor is described below for a bench-scaleapplication. A full-scale application is consistent therewith and wouldbe understood by those skilled in the art made aware of this invention.With reference to FIGS. 2A-B, a bench-scale MBfR system can comprisehollow-fiber membranes, hydrogen gas supply system, substrate and bufferstorage tank, and associated feed pump, flow meter, stir plate, andeffluent collection tank. An apparatus of the sort presented in FIG. 2Awas constructed using a section of polycarbonate pipe, capped on eachend with polycarbonate plates. Hollow-fiber membranes are attached tothe top plate. A stir-bar at the bottom of the reactor keeps the reactorwell-mixed. Hydrogen is supplied to the fibers through a manifold in theplate. A second “dead-end” manifold on the top plate collects the distalends of the fibers. This manifold is normally sealed, but can be openedto purge the fibers. The reactor specifications are provided below.

MBfR Specifications Net reactor volume 300 mL Height 9 cm Diameter 7 cmHeight of fiber support 6 cm Number of individual fibers 51 Total numberof holes in support grid 130 Number of fibers per grid hole 3 Totallength of fibers 23.4 m Total surface area of fibers 206 cm²

A total of 51 individual hollow fibers are provided, with a totalsurface area of about 206 cm². Mixing provided by a stir-bar improvesmass transfer to the biofilm, prevents the fibers from stickingtogether, and minimizes fouling of the membranes by excess biomassaccumulation. Hydrogen gas is supplied by a pressurized gas cylinder. Asillustrated in FIG. 1, hydrogen gas is fed to one end of the reactor,filling the inside of the fibers and diffusing through the membranes.The hydrogen pressure is preferably maintained below the bubble-point ofthe membrane, eliminating the formation of a hydrogen atmosphere withinthe bioreactor.

In a conventional autohydrogenotrophic system, a fixed-film orfluidized-bed biofilm reactor, in which all substrates (such as nitrateand hydrogen) are transferred from the liquid phase into the biofilm, isutilized. An apparatus such as that provided in FIG. 2A scheme offers animportant advantage over convention. Since the biofilm is on the surfaceof the hollow fiber, the hydrogen flux goes directly into the biofilm.Nearly 100% utilization of hydrogen is attained, making the process moreeconomically favorable and safer. Preliminary studies were conducted onnitrate and perchlorate reduction by an autohydrogenotrophic MBfR andestablish certain principles pertaining to this invention. The membranefibers used therewith were installed in a tube reactor, of the '262patent, about 1 m long. The prototype contained 83 fibers that provided750 Cm² of surface area for biofilm attachment (specific surface areawas 180 m⁻¹). Feed and recycling flow rates during the experiments werefixed at 10 and 1,750 ml/min, respectively. The recycle controlled theliquid flow velocity for good mass transport and to prevent fiberclumping. The system was seeded initially with Ralstonia eutropha, but adiverse mixed culture developed over time.

As described in the aforementioned '262 patent, as an electron donor,hydrogen gas is oxidized by species of hydrogen-oxidizing bacteria withrelease of electrons for reduction of contaminant(s). For example,nitrate is reduced in a step wise fashion to innocuous nitrogen gas:

NO₃⁻ + 2H⁺ + 2e⁻ =  = NO₂⁻ + H₂ O NO₂⁻ + H⁺ + e⁻ =  = NO + OH⁻NO + H⁺ + e⁻ =  = 0.5N₂O + 0.5H₂O$\underset{\_}{{{0.5N_{2}O} + H^{+} + e^{-}}=={{0.5N_{2}} + {0.5H_{2}O}}}$NO₃⁻ + 5H⁺ + 5e⁻ =  = 0.5N₂ + 2H₂O + OH⁻  (overall)

With reference to the results provided in the '262 patent, the influentnitrate concentrations were 10 and 12.5 mg N/l for the first and secondsteady states, respectively. At steady-state with a liquid retentiontime of 40 min, there were achieved the desired partial removals ofnitrate between 76 and 92% with effluent hydrogen concentration as lowas 9 μgH₂/L. The nitrate flux was as high as 1 g N/m²-d due possibly tothe “counter-diffusion” type of substrate transfer. Fiber clumping, andthe biofilm detachment rate from the fibers were very low, about0.015/day.

For each steady state, nonsteady-state experiments were run to test theMBfRs response to nitrate loading and hydrogen pressure. Each short-termstudy lasted for more than three liquid retention times to allow theformation of a pseudo-steady state in the reactor. The nonsteady-stateexperiments show that adjustments to the hydrogen pressure to the hollowfibers easily and rapidly controlled the effluent nitrate concentrationand % nitrogen removal. For example, a loading of 0.1 mgN/cm²-d (=1gN/m²-d) gave nearly 100% NO₃ ⁻ removal when the hydrogen pressure tothe fibers was 6.6 psi (0.45 atm), but reducing the hydrogen pressure to3 psi (0.2 atm) gave partial removal of 50%. For drinking-watertreatment, the goal is to keep the effluent NO₃ ⁻—N below the standardof 10 mgN/L, which makes partial removal feasible and desirable. Otherapplications may require full nitrate removal and, therefore, higherhydrogen pressure.

Representative of other oxidized contaminants treated with the presentinvention, perchlorate ion (ClO₄ ⁻) can originate from a variety ofammonium, potassium, magnesium, or sodium salts. Ammonium perchlorate,for example, is a primary ingredient of solid rocket fuel. The shortshelf-life of rocket fuel has created an environmental concern given thelarge volume of perchlorate-containing wastes generated over the yearsby unused fuel. At least 20 states have confirmed perchloratecontamination, and more sites may be found, as perchlorate has been usedor manufactured in up to 40 states. Perchlorate is understood to inhibitthyroid function and is suspect in various other health-related issues.The State of California, recognizing the problem, recently lowered itsperchlorate drinking water action level from 18 to 4 μg/L. Even so, arecent toxicological and risk characterization study by theEnvironmental Protection Agency suggests 1 μg/L as a treatment goal fordrinking water.

Perchlorate is not removed by conventional physical-chemical watertreatment techniques, and other processes, such as ion exchange,electrodialysis, and reverse osmosis are costly and result in aconcentrated perchlorate waste stream that still requires disposal. As aresult, perchlorate contamination of groundwaters continues to be anenvironmental issue. Perchlorate can be reduced, however, to chloride byperchlorate-reducing bacteria, which use perchlorate as an electronacceptor for growth. Perchlorate-reducing bacteria are readilyobtainable in the environment, have a wide range of metaboliccapabilities, such as aerobic growth and denitrification, and do notrequire specialized growth conditions-all attributes suitable for aperchlorate treatment system. Recent work has shown that bioreactors canreduce perchlorate to below 4 μg/L when the initial concentration ishigh or when the reactor has been previously operated at highperchlorate concentrations. However, low initial perchlorateconcentrations, in the μg/L range, may preclude biomass growth onperchlorate as the sole acceptor electron growth.

Even so, microbial treatments such as those described in the '262 patentleave several concerns as open issues. For instance, whilenitrate/nitrite reduction is discussed, therein, and other oxidizedcontaminants are mentioned as likewise treatable, concurrent treatmentof multiple contaminants remains unaddressed. The '262 patent does notdisclose concurrent treatment, and work thereafter appears to indicatefull nitrate removal is required for perchlorate reduction to usefullevels. Regardless, the present invention can be used for concurrenttreatment of multiple oxidized contaminants, as part of a comprehensivetreatment methodology.

To demonstrate related methods of this invention, the same laboratoryprototype reactor described above was used with addition of perchlorate.Immediate perchlorate removal (roughly 40% removal from 1,600 μg/L) wasobserved, and the removal increased over two weeks to nearly 100%,showing that the autotrophic denitrifiers were capable of reducingperchlorate, but that the growth of bacteria with better capability toremove perchlorate occurred over time. Perchlorate reduction toinnocuous, chloride ion is believed to be achieved via an 8-electronpathway:

ClO₄⁻ + 2H⁺ + 2e⁻ =  = ClO₃⁻ + H₂O ClO₃⁻ + 2H⁺ + 2e⁻ =  = ClO₂⁻ + H₂OClO₂⁻ =  = O₂ + Cl⁻$\underset{\_}{{O_{2} + {4H^{+}} + {4e^{-}}}=={2H_{2}O}}$ClO₄⁻ + 8H⁺ + 8e⁻ =  = Cl⁻ + 4H₂O  (overall)

Perchlorate removal was somewhat affected by a high nitrateconcentration in the reactor. NO₃ ⁻—N greater than about 0.1 to 0.2 mg/Lslowed perchlorate reduction, and NO₃ ⁻—N above about 0.5 mg/L slowedperchlorate reduction by 50% or more. On the other hand, increasing thehydrogen pressure increased perchlorate removal, and the effect was muchmore dramatic than for denitrification.

After completing systematic studies with a laboratory prototype, it wasused with perchlorate-contaminated groundwater: the groundwater with itsnormal ClO₄ ⁻ concentration of 6 μg/L, and also with a ClO₄ ⁻concentration spiked to 100 or 50 μg/L. Removal of perchlorate below the4 μg/L action level was observed in all cases. Stoichiometriccomputations based on the removals of all electron acceptors in thegroundwater (i.e., 24 mg/L of NO₃ ⁻—N, 6 mg/L of O₂, and 60 μg/L of ClO₄⁻) show that hydrogen utilization is almost exactly equivalent toacceptor reduction—indicating that no hydrogen is wasted, aconsideration for good economy and safe operation.

Hydrogen-oxidizing bacteria are known to those skilled in the art andwould be understood by those made aware of this invention as includingboth hydrogen-oxidizing, autotrophic bacteria, as well as those bacteriaalso able to utilize organic carbon and other energy sources in additionto hydrogen. Without restriction to any one theory or mode of operation,this invention can be used to remove perchlorate and othernon-nitrogenous oxidized contaminants with sufficient levels of suchcontaminants as electron acceptors or in the presence of anotherelectron acceptor. A primary electron acceptor is an oxidized componentreduced in conjunction with the aforementioned oxidation (e.g.,perchlorate, etc.), such reduction at least in part sufficient tosustain a viable biomass within the aqueous system. A component capableof providing such a function would be understood by those skilled in theart and made aware of this invention. Such reduction providing energyfor growth can be referred to as a dissimilatory reduction, withperchlorate as a secondary acceptor in the context of this methodology.Without limitation, a primary electron acceptor component can beselected from oxygen and nitrate anion—either one of which preferablyhas a system concentration at least in part sufficient to supportaccumulation of bacteria—or a combination thereof.

Regardless of the chemical identity of such a component functioning as aprimary electron acceptor, such a component can be introduced to such asystem prior to introduction of a perchlorate component, such that asustainable biomass can be achieved. Alternatively, such a component canbe introduced concurrent with that of the perchlorate component to thesystem. Accordingly, with regard to the latter, the primary electronacceptor component (e.g., nitrate anion) can be influent to the systemwith a waste stream comprising the subject perchlorate component. Asillustrated by several of the following examples, the present inventioncan be utilized with influent perchlorate concentrations greater thanabout 100 μg/L or below which would not otherwise—in the absence of aprimary acceptor—support biofilm accumulation. Regardless, effluentconcentrations can be less than about 4 μg/L, meeting applicable stateand/or federal guidelines.

Without limitation, as provided by one of several embodiments, theoxidized contaminant can be perchlorate, chlorate, chlorite, or acombination of such contaminants. Other oxidized contaminants removed bythe present methodology include those described herein. As demonstratedby several examples below, repetitious or continuous introduction of theoxidized contaminant can promote concurrent removal of the primaryelectron acceptor. Likewise, such introduction can enhance removal ofthe oxidized contaminant, such enhancement as can be expressed in termsof rate of or time for removal. Without limitation, as presented underconditions of surface or groundwater contamination, the primary electronacceptor component and the oxidized contaminant are influent to thesystem. Regardless, such a system can be used in conjunction withanother water treatment process; that is, as an adjunct to anothersystem for enhanced or complimentary removal of contaminants.

Schematically, such methodologies of this invention can be consideredwith reference to FIG. 3. Primary electron acceptor and oxidizedcontaminant components can, optionally, be introduced at various levelsrelative one to another, as indicated. Contact of a system comprisinghydrogen-oxidizing bacteria provides corresponding reduction and removalof the components. Such a method can be employed without restriction toany one biofilm reactor apparatus, fiber or membrane configuration,consistent with the broader aspects and considerations of thisinvention.

Regardless of the presence of perchlorate or other such oxidizedcontaminants (see, Example 7), the present invention can also beutilized for wastewater treatment. As such, the apparatus and methodsdescribed herein meet several goals and objectives. The need foradditional of an extraneous organic electron donor is eliminated,thereby minimizing excess sludge production, chemical costs, handlingand toxicity concerns. Further, this invention can be easily integratedinto a variety of wastewater treatment systems. More specifically,integration into existing or new activated-sludge systems can beachieved by either (1) using this invention for tertiary denitrificationor post treatment to remove nitrate (or nitrite) remaining afterconventional treatments such as pre-denitrification, or (2)incorporating an apparatus and/or methodology of this invention directlyinto a pre-denitrification system to enhance performance withoutconstruction of an adjunct tertiary system. The goal of tertiarydenitrification with the MBfR is to reduce the effluent NO₃ ⁻concentration to an advanced-treatment standard (e.g., ≦1 mgN/L), inconjunction with a conventional pre-denitrification process which canbring the NO₃ ⁻ concentration down to about 10-about 15 mgN/L. FIG. 4illustrates how a tertiary system comprising this invention could beemployed in a typical post-treatment scenario. This application issimilar to the drinking-water settings that have been investigated fordenitrification, although two differences are evident. First, theeffluent criterion for NO₃ ⁻ is lower for wastewater treatment: ≦1 mgN/Lversus well below the drinking-water standard of 10 mgN/L. Second, theinfluent to the MBfR is likely to contain a significant concentration ofsuspended solids, which are absent or negligible in drinking-watertreatment. The physical configuration of an apparatus of this inventioncan accommodate influent solids without fouling the membrane components.One advantage of using a H₂-based MBfR in tertiary denitrification isthat the autotrophic biomass yield is low, which means that the solidsconcentration in the effluent will be low, thereby minimizing solidsload to downstream filters, if employed. If no downstream filters are inplace, the effluent suspended solids, COD, and N due to released biomasswill be low.

Alternatively integrating an MBfR of this invention intopre-denitrification obviates the need to construct anytertiary-treatment apparatus or facility. The benefits for capital costsand space are obvious. FIG. 5 schematically illustrates how MBfR unitscould be integrated into a multiple-pass (e.g., with return-activatedsludge, RAS, and/or a primary effluent, PE, component),pre-denitrification system known in the art to augment the capacity forNO₃ ⁻ removal from wastewater. Use of an inventive apparatus inconjunction with an anoxic component of such a pre-denitrificationsystem, with alternating passes to and from an oxic component, providesa low oxidized nitrogen effluent for routing to a final settling tank(FST). Integration creates a hybrid biofilm/suspended-growth system inwhich the biofilm is dominated by H₂-oxidizing autotrophs, while thesuspended bacteria are BOD-oxidizing heterotrophs and autotrophicnitrifiers. Achieving integration involves a number of technicalchallenges: preventing fouling of the membranes from the suspendedbiomass and influent solids, good mass transfer to the membranes,biofilm control on the membranes, controlling the oxygen concentrationto allow good nitrification, but not create a large H₂ demand to reduceO₂, and locating the MBfR units in the best place to gain very loweffluent NO₃ ⁻ concentration while using the influent BOD as much aspossible for denitrification.

EXAMPLES OF THE INVENTION

The following non-limiting examples and data illustrate various aspectsand features relating to the apparatus and methods of this invention,including the treatment of nitrate, perchlorate and other oxidizedcontaminants, as can be achieved through the techniques describedherein. While the utility of this invention is illustrated through useof one or more articles, devices or apparatus that can be usedtherewith, it will be understood by those skilled in the art thatcomparable results are obtainable with various other articles/devicesand apparatus, as are commensurate with the scope of this invention.

With regard to the present examples, perchlorate was analyzed by ionchromatography (IC) using a Dionex DX-320 (pilot) or 4000i (bench) withconductivity detection. An AS-16 or AS-11 column was used followed EPAMethod 314.0. The lowest standard used during calibration was 2 μg/L.All anions other than perchlorate (i.e., chloride, chlorate, chlorite,nitrate, among others) were analyzed on the same systems based on EPAMethod 300.1 modified for a hydroxide-selective column. Dissolvedhydrogen was analyzed with a reduction gas analyzer (Trace AnalyticalRGA3) using a headspace analysis described in the literature.

Demonstrating various aspects of the present invention, the data ofexamples 1-7 was obtained using a hollow-fiber membrane biofilm reactorof the prior art. Comparable results are obtainable with variousapparatus configured and ascribed herein, whether or not a particularoxidized contaminant is utilized alone or in the presence of anotherelectron acceptor, as would be understood by those skilled in the artmade aware of this invention.

Example 1

In drinking-water treatment, a goal is to remove NO₃ ⁻ to below thestandard, which typically is 10 mgN/L. Therefore, partial NO₃ ⁻ removalto levels below the standard is acceptable, as long as partial removalis reliable and no other water-quality problems are introduced. Partialor full NO₃ ⁻ (and nitrite) removal can be achieved and easilycontrollable. Adjusting the H₂ pressure to the interior of the membranessimply and reliably controlled the effluent concentration of NO₃ ⁻—N.Within the H₂-pressure range of about 0.15 to 0.6 atmospheres, theeffluent NO₃ ⁻ concentration could be controlled systematically fromless than 0.1 mgN/L for the higher H₂ pressures and low to moderate NO₃⁻ surface loading to 10 mgN/L for the lower H₂ pressure and a high NO₃ ⁻surface loading. Increasing the H₂ pressure inside the membranesincreased the H₂-delivery capacity, making it possible to drive the NO₃⁻ concentration to very low level, treat a higher surface loading of NO₃⁻, or a combination of both. In most cases, the NO₂ ⁻ concentration wasless than 1 mgN/L, and increasing the H₂ pressure made it possible todrive effluent NO₂ ⁻ to less than 0.1 mgN/L.

Generally, denitrification also showed that the biofilm that accumulatedon the outside of the membranes in the bench-scale MBfR was dense andstrong. The specific detachment rate was very low (<0.02/d), and theeffluent biomass concentration was correspondingly low (c. 1 mg/L). Thebiofilm produced some soluble microbial products, giving a typicaleffluent BDOC of 0.5 mg/L, which can be eliminated by downstreambiofiltration. The net acid consumption of denitrification requiredattention to pH buffering, but this situation is true for alldenitrification processes.

Example 2a

Biological perchlorate reduction was studied in a denitrifying MBfR. TheMBfR medium was based on tap water, and the reactor was seeded withbacteria from an MBfR used in a previous denitrification study. The seedincluded a mixed microbial population of autotrophic, denitrifyingbacteria. After reaching steady-state with nitrate, and without havinghad any previous exposure to perchlorate, the MBfR influent wassupplemented with 1,000 to 1,800 μg/L perchlorate. The reactor hydraulicdetention time was 45 minutes, and it had a high recirculation rate topromote completely-mixed conditions. Initial nitrate removal was around98%, while initial perchlorate reduction was 60% (data not shown).Perchlorate reduction increased to 99% over 18 days, while the nitratereduction rate remained approximately the same. The slow improvement inperchlorate reduction suggests an enrichment for specialized,perchlorate-reducing bacteria.

Example 2b

The MBfR described above was tested with a perchlorate-contaminatedgroundwater collected from a well owned and operated by the SuburbanWater Company, located in the Main San Gabriel Basin, California. Nochemical additions, other than perchlorate and hydrogen, were madeduring the groundwater experiments. The influent nitrate concentrationwas 2.6 to 3.0 mgN/L. Three phases of testing were used over a period of28 days. First, the groundwater was applied for 7 days with its naturalperchlorate concentration of 6 μg/L, representing a low-perchloratescenario. Second, the feed water was spiked with 100-μg/L perchloratefor 15 days, representing a high range of perchlorate in mostcontaminated groundwaters in Southern California. Finally, the reactorfeed was spiked with 50 μg/L perchlorate for 5 days, representing amid-range of perchlorate contamination. The reactor operating conditionswere similar to those described above. For all three phases of the test,the effluent perchlorate varied from non-detect (less than 2 μg/L) to4.5 μg/L, and the effluent nitrate varied from 13 to 32 μgN/L, whichcorresponds to at least 99 percent removals of perchlorate and nitrate.

The groundwater experiments clearly demonstrate the feasibility of usingthe MBfR to remove perchlorate from groundwater that also containsnitrate. The reactor consistently achieved removals at or below the MRLof 4 μg/L over a four-week period. The reactor also responded well tosudden changes in perchlorate concentrations. For example, when theinfluent concentration was suddenly increased from 6 μg/L to 100 μg/L,the effluent perchlorate concentrations did not increase above 4 μg/L.

Example 2c

The above MBfR was switched from tap water to a minimal medium preparedfrom reverse-osmosis-treated water. Both media contained 5 mgN/L nitrateand 1,000 μg/L perchlorate. Prior to starting the reverse-osmosismedium, the effluent perchlorate was non-detect. Immediately afterstarting the minimal medium, the effluent perchlorate concentrationincreased from non-detect to around 300 μg/L. The rate of nitratereduction was not affected. Over several months, the perchloratereduction rate further deteriorated, with effluent concentrationsexceeding 900 μg/L. However, when the tap water medium was restored, theeffluent perchlorate decreased to non-detect after 16 days. This“acclimation” time period is similar to the 18 days it took to achievemaximum perchlorate removal when perchlorate was first introduced intothe hydrogen reactor during the screening experiment. On the 16^(th)day, RO-medium was reintroduced and effluent perchlorate increased to360 μg/L by the next day, reaching 500 μg/L on day 21. At the end of day21, tap-water medium was introduced a second time, and the next dayperchlorate had returned to non-detectable levels. During all 21 days,the effluent nitrate concentration remained practically unchanged. Thisexperiment shows that the minimal media lacked for perchloratereduction, but not for denitrification. The slow disappearance ofperchlorate reduction suggests the loss of specializedperchlorate-reducing bacteria. The subsequent increase of perchloratereduction in the presence of tap water medium suggests a renewedenrichment of perchlorate-reducing bacteria.

Example 3a

Dechloromonas sp. PC1 is an autotrophic, hydrogen-oxidizing,perchlorate-reducing and denitrifying bacterium isolated from thereactor described in Example 1. Batch tests were carried out todetermine the kinetic parameters q_(max), Y, and K for PC1 (GenBankaccession number AY126452). The kinetic parameters were determined forautotrophic growth using hydrogen as an electron donor. The Y andq_(max) were determined using batch experiments with high initialacceptor and low initial biomass concentrations. The K was determinedusing batch non-growth tests with low initial biomass and acceptorconcentrations. The experiments used 1-L bottles filled with 200 mL ofmedia or 160 mL serum bottles filled with 25 mL of media, capped withbutyl rubber stoppers, vacuum degassed, and filled with a gas mixture of95% hydrogen and 5% CO₂ (for q_(max) and Y) or with pure hydrogen (forK). The bottles were shaken on their side at 200 rpm. The experimentswere carried out at least in triplicate. The growth medium contained,per liter: 1.386 g Na₂HPO₄, 0.849 g KH₂PO₄, 0.1 g (NH₄)₂SO₄, 0.2 gMgSO₄.7H₂O, 1 mg CaCl₂.2H₂O, and 1 mg FeSO₄.7H₂O. The trace mineralsolution is described in the literature. The K experiments were carriedout in a 12-mM phosphate buffer at pH of 7 with no nutrients or traceminerals. The pH was adjusted using 1 M NaOH for a final pH of 7.0.Curve fitting was used to estimate kinetic parameters q_(max) and K forPC1 using a finite-differences solution of the substrate-utilization andbiomass-growth equations:

${\frac{\mathbb{d}S}{\mathbb{d}t} = {{- \frac{q_{\max}S}{S + K}}X}},{and}$$\frac{\mathbb{d}X}{\mathbb{d}t} = {{\frac{{Yq}_{\max}S}{S + K}X} - {{bX} \cdot}}$Such relationships neglect competitive inhibition from chlorate duringperchlorate reduction, providing a q_(max) for perchlorate is an“apparent” value, valid only for the perchlorate range for which it wasdetermined.

Example 3b

As shown in Table 1, the yields for perchlorate were very similar tothose for nitrate. This is consistent with the similar Gibb's freeenergy at pH 7 (ΔGo) for perchlorate and nitrate reduction with hydrogen(118 and 112 kJ/eq e-H2, respectively). The q_(max) for nitratereduction was around 6 times higher than for perchlorate, on anelectron-equivalent (or hydrogen-accepting) basis, demonstrating growthon nitrate much faster that on perchlorate. The K value for perchloratewas 0.15 mg/L, two orders of magnitude lower than values from theliterature for other perchlorate-reducing bacteria.

Based on the kinetic parameters, the S_(min) for perchlorate is 40 μg/L.This is an approximate value, since q_(max) does not include competitiveinhibition with chlorate. It is unlikely that the actual S_(min) wouldbe much less than this value, suggesting perchlorate can not be reducedto 4 μg/L and/or below levels permissible under regulation withperchlorate as the sole electron acceptor.

TABLE 1 Kinetic parameters for Dechloromonas sp. PC1 q_(max) Y K S_(min)S (eq e⁻H₂/g X-day) (gX/eq e⁻H₂) (mg/L) (μg/L) ClO₄ ⁻ 0.25 2.88 0.15 40NO₃ ⁻ 1.43 2.46 >0.05 <2 Notes: (1) “eq e⁻H₂” = equivalent of electronsfrom hydrogen; (2) 1 eq e⁻H₂/ = 1 g H₂(3) b = 0.1 1/dayKinetic parameters found for other perchlorate-reducing bacterialsuggest the same. See, Logan, B. E., H. S. Zhang, P. Mulvaney, M. G.Milner, I. M. Head and R. F. Unz (2001). Kinetics of perchlorate- andchlorate-respiring bacteria. Applied and Environmental Microbiology67(6): 2499-2506. Other experiments (not shown) demonstrate that nitrateor oxygen can serve as primary acceptors that allow concurrentperchlorate removal. Even if the perchlorate concentration is lowcompared to nitrate or oxygen, perchlorate helps select for aperchlorate-reducing population. Since most wastewaters, groundwatersand surface waters contain nitrate, oxygen, or both, the MBfR is likelyto be effective for a wide range of field applications.

Example 4a

Two bench-scale MBfRs were seeded with a mixed culture from anotherreactor. The primary acceptor for one reactor was 8-mg/L oxygen, and 5mgN/L nitrate (plus a minor influent O₂ concentration of about 6 mg/L)for the other. A minimal medium based on reverse-osmosis water was used.The physical characteristics are summarized in Table 2, below. A highrecirculation rate provided completely mixed conditions. After reachingeffluent steady state with the primary acceptors, perchlorate was addedto the influent: 1,000 μg/L perchlorate for the oxygen reactor, and 100μg/L for the nitrate reactor.

TABLE 2 Bench- scale reactor characteristics PARAMETER BENCH-SCALE Feedrate 1 mL/min Recirculation ratio 150 Detention time 24 min Number ofmodules 1 Module length 25 cm Module diameter 0.6 cm Number of fibersper module 33 Total fiber surface area 72.3 cm²

Example 4b

The two bench-scale MBfRs of example 3a were operated for 20 days with5-mgN/L nitrate or 8-mg/L oxygen. In the nitrate reactor, the effluentnitrate reached 0.01 mgN/L after around 10 days. In the MBfR with oxygenand no nitrate, the DO levels were below 0.1 mg/L after 4 days ofoperation. After 20 days, 100-μg/L and 1,000-μg/L perchlorate was addedto the nitrate and oxygen reactors, respectively. In the nitratereactor, the initial removal was 30%, but it increased to more than 90%after 4 days. In the oxygen reactor, the initial removal was 5%, but itincreased to more than 99% after 12 days. These results illustrate thateven low levels of perchlorate can provide a selective pressure forperchlorate-reducing bacteria, dramatically improving removals. Also, itshows that oxygen can serve as a primary acceptor for perchloratereduction. Reference is also made to examples 6a-b below.

Example 5

With reference to the membrane configuration of FIG. 1, and theapparatus of FIGS. 2A and 2B, hollow fiber membranes can be about 280 μmin diameter with an approximate 40-μm wall, are preferably but notrequired to be made of two materials: a 1-μm layer of dense polyurethaneencased within microporous polyethylene (FIG. 1). Because the fibermaterial is hydrophobic, the pores remain dry and do not foul. The densepolyurethane layer prevents bubbling at higher gas pressures, allowing awide range of gas of pressures that offer a high degree of control overthe hydrogen-delivery rate. A scanning electron micrograph (SEM) imageof the fiber wall and a confocal laser scanning micrograph (CLSM) imageof biofilm on the hollow-fiber membrane are consistent with thepreceding and confirm biomass accumulation.

Example 6a

Some hydrogen-oxidizing, perchlorate-reducing bacteria (PCRB) candenitrify and reduce perchlorate concurrently, with nitrate as a primaryacceptor. This example demonstrates various aspects of this inventionand explore whether PCRB or non-perchlorate-reducing denitrifierspredominate when an environmental inoculum is used. The microbialecology of mixed-culture, perchlorate-reducing and denitrifying MBfRswas investigated using activity tests and confirmed using moleculartechniques.

Hydrogen is supplied through hollow-fiber-membranes. Water containing aprimary acceptor, either nitrate or oxygen, is recirculated past theexterior of the membranes, and a biofilm grows on the membrane surface.Five identical MBfRs were used. Nitrate was the primary acceptor forreactors R1 through R4, and it was oxygen for R5. The detention time was25 minutes, and the inoculum was a small amount of biofilm from an MBfRtreating groundwater with 5 mgN/L nitrate and 60 μg/L perchlorate. Afterreaching steady state with the primary acceptor, 0, 100, 1,000, and10,000 μg/L of perchlorate were added to the reactors R1, R2, R3, andR4, respectively. Table 3 shows the experimental conditions.

TABLE 3 NO₃ ⁻ ClO₄ ⁻ O₂ conc. Sample conc. (mg/l) conc. (mg/l) (mg/l)R1-4 (May 21) 5.0 — — R5 (May 21) — — 8.0 R1 (June 13) 5.0 — — R2 (June13) 5.0 0.1 — R3 (June 13) 5.0 1.0 — R4 (June 13) 5.0 10.0 — R5 (June13) — 1.0 8.0

Example 6b

For all reactors, the primary acceptor was completely reduced within 5days. Perchlorate was reduced completely (R2 and R5) or by about 60% (R3and R4) within 2 weeks of its addition. Activity tests were carried outto explore the ecology of the MBfRs. Reactors 1, 2, and 4 werechallenged with a medium containing 10,000-μg/L perchlorate and 5-mg/Lnitrate. The average removals at the end of the tests are plotted inFIG. 10. R3 and R5 were not operating at the time. These results show ahigher perchlorate-reducing activity in the reactors that had higherinfluent perchlorate, suggesting enrichment for perchlorate-reducingbacteria. Further studies of the microbial community using DenaturingGradient Gel Electrophoresis (DGGE) suggest an increasing abundance of aperchlorate-reducing isolate for the reactors with increasing influentperchlorate concentrations. Tests using Fluorescent In-SituHybridization to quantify bacteria matching the above DGGE band confirmits enrichment with higher influent perchlorate concentrations.

Example 7

Another reactor was tested for removal of several other oxidizeddrinking water contaminants. In all tests, the influent included 5-mg/Lnitrate or 8 mg/L O₂ as a primary electron accepting substrates, plus anoxidized contaminant, i.e., “compound” in Table 4. The reactor wasseeded with a mixed culture of autotrophic, denitrifying bacteria from aprevious denitrification study and was operated at a pH of 7 and a25-minute hydraulic detention time. A high recirculation rate was usedto simulate mixed or stirred conditions. The experiments for allcontaminants lasted 10 hydraulic detention times. No attempt was made tooptimize contaminant reduction; an objective was simply to demonstratereduction by a denitrifying or oxygen-reducing mixed culture. Theresults are summarized in Table 4. In all the tests, over 99 percent ofthe nitrate and oxygen was reduced.

{TABLE 4 Removal Efficiency (%) Probable Reduction O₂ NO₃ ⁻ CompoundReaction(s) Reactor Reactor Arsenate H₂AsO₄ ⁻ + >50 >50 H₂ + H⁺ →H₃AsO₃ + H₂O Bromate BrO₃ ⁻ + 3H₂ → >95 >95 Br⁻ + 3H₂O Chlorate ClO₃ ⁻ +3H₂ → >95 29 Cl⁻ + 3H₂O Chlorite ClO₂ ⁻ + 2H₂ → >75 67 Cl⁻ + 2H₂OChromate HCrO₄ ⁻ + 1.5H₂ + >75 >75 2H⁺ → Cr(OH)₃ + H₂O Dichloro-CH₂Cl₂ + 2H₂ → 38 45 methane CH₄ + 2H⁺ + 2Cl⁻ Nitrate NO₃ ⁻ + 2.5H₂ +Not tested >99 H⁺ → 0.5N₂ + 3H₂O Perchlorate ClO₄ ⁻ + 4H₂ → >98 36 Cl⁻ +4H₂O Selenate SeO₄ ²⁻ + 3H₂ + 67 74 2H⁺ → Se° + 4H₂O SeO₄ ²⁻ + 2H₂ + H⁺→ HSeO₃ ⁻ + H₂O 93 57 Selenite HSeO₃ ⁻ + 2H₂ + H⁺ → Se° + 3H₂O

The results show the chlorate and chlorite contaminants are reducedunder denitrifying and oxygen reducing conditions—consistent and inaccordance with the results obtained with perchlorate. Likewise andwithout limitation, various other contaminants (e.g., bromate, selenate,selenite, nitrite, etc.) were also reduced and removed, as shown inTable 4. With greater acclimation times, lower input concentrationsand/or reactor optimization, higher efficiencies can be obtained.

Example 8

Preliminary studies were carried out on wastewater denitrification withan MBfR apparatus in accordance with FIG. 2A. An open matrix or spatialarrangement defined by the membrane configuration allows mixed liquor tomove between the membrane fibers without being filtered out or foulingthe membrane surface. The influent contained the effluent from thefirst-stage of the multiple-stage pre-denitrification plant in New YorkCity. The influent to the MBfR had a NO₃ ⁻ concentration of about10-about 20 mgN/L. The flow rate was 2.3 L/d, giving an empty-bedhydraulic retention time of 3 h. No inoculum was provided before feedingthe wastewater to the MBfR.

Denitrification in the MBfR started immediately and achieved a highlevel of denitrification within a few days. Effluent NO₃ ⁻ was driven tobelow about 1 mgN/L, and H₂ pressure gave sensitive control of thedenitrification capacity. For example, when the H₂ pressure was only 2psi (0.14 atm) and influent NO₃ ⁻ was 13 mgN/L, the effluent NO₃ ⁻ was0.85 mgN/L, giving a NO₃ ⁻ flux of 1.4 gN/m²-d. Increasing the H₂pressure to 5 psi (0.34 atm) when the influent NO₃ ⁻ was 16.4 mgN/L gaveeffluent NO₃ ⁻ of only 0.4 mgN/L, with a NO₃ ⁻ flux of 1.8 gN/m²-d.

Despite the open-matrix configuration, extended operation withoutsufficient mixing and turbulence can lead to excess biofilm orsuspended-solids accumulation, causing some membrane fibers to clumptogether with reduction of biofilm surface area and the mass-transportrate to the biofilm. For example, a H₂ pressure of 5 psi (0.34 atm) gavea nominal NO₃ ⁻ flux of 1 gN/m²-d and had effluent NO₃ ⁻ and NO₂ ⁻concentrations of 3.6 and 1.6 mgN/L, respectively, after clumping.

An H₂-based MBfR has been proven for the reduction of nitrate andperchlorate and other oxidized contaminants in drinking water andgroundwater settings. However, in light of this invention, use ofhydrogen as an electron donor may have most extensive application foradvanced nitrogen removal in wastewater treatment, where existingapproaches full to achieve the goals of advanced-N removal; have severeproblems of cost, reliability, and safety; or both. By utilizing H₂ gasas the electron donor to drive denitrification, an MBfR of thisinvention and related methods completely eliminate an added organicelectron donor, which overcomes major problems: a large increase inexcess biomass generation, over- or under-dosing of donor, safetyconcerns, and relying on specialized methanotrophs. In addition, such anapparatus simple to operate, and it can be used for tertiarydenitrification or integrated into a pre-denitrification process.Preliminary results show that autotrophic denitrifiers accumulaterapidly in the wastewater setting, the MBfR can drive NO₃ ⁻concentrations below 1 mgN/L, and the H₂ pressure controls the NO₃ ⁻flux.

With reference to the preceding, a range of other oxidized contaminantscan be reduced and/or removed from an aqueous medium, such contaminantsincluding but not limited to oxidized species of uranium, neptunium,sulfur, cadmium, and nickel, as well as other halogenated hydrocarboncompounds. Such contaminants can be treated/removed as would beunderstood by those skilled in the art made aware of this inventionusing the procedures described herein for straight-forward modificationsthereof, such modifications as would also be known to such individualswithout undue experimentation.

1. An apparatus, comprising: a support grid having a plurality ofopenings extending through the grid; a plurality of hydrogen permeablehollow fiber membrane components, each said membrane component having afirst end, a second end, and a passage; wherein the first ends of atleast a portion of the plurality of membrane components are coupled to afirst of the plurality of openings and extend therethrough; and an inletcomponent for coupling said plurality of membrane components to ahydrogen source.
 2. The apparatus of claim 1 wherein each hollow fibermembrane is sealed at one end.
 3. The apparatus of claim 1 wherein saidinlet component comprises a manifold.
 4. The apparatus of claim 2wherein said membrane components are positioned in a row configuration.5. The apparatus of claim 4 wherein said membrane components arepositioned in a configuration of rows and columns.
 6. The apparatus ofclaim 1 wherein each membrane component comprises a substantiallynon-porous member.
 7. The apparatus of claim 6 wherein each saidmembrane component comprises inner and outer layers having a firstdensity and a layer therebetween having a second density greater thansaid first density.
 8. The apparatus of claim 7 wherein said layerbetween said inner and outer layers is substantially non-porous.
 9. Theapparatus of claim 1 in a container.
 10. The apparatus of claim 9wherein said container is an activated sludge tank.
 11. A method fortreating a wastewater system comprising solid particles, the methodcomprising: providing an apparatus according to claim
 1. 12. The methodof claim 11, further comprising contacting the apparatus with hydrogengas.
 13. The method of claim 12, wherein the hydrogen gas is contactedwith the apparatus at a pressure of between 0.15 and 0.6 atmospheres.14. The method of claim 12, wherein during operation, NO₃ ⁻ in thewastewater is maintained below 10 mgN/L.
 15. The method of claim 12,wherein during operation, NO₃ ⁻ in the wastewater is maintained below 1mgN/L.
 16. The method of claim 12, wherein during operation, NO₃ ⁻ inthe wastewater is maintained below 0.1 mgN/L.
 17. The apparatus of claim1, wherein the second end of at least a portion of the plurality ofmembrane components are coupled to a second of the plurality ofopenings.
 18. The apparatus of claim 17, wherein the second end of atleast a portion of the plurality of membrane components extend throughthe plurality of openings.
 19. The apparatus of claim 1, furthercomprising a tank having an upper end for enclosing said support gridand plurality of membrane components, wherein said support grid issuspended from the tank upper end.
 20. The apparatus of claim 19,wherein said inlet is located at the upper end of the tank.
 21. Theapparatus of claim 1, wherein said plurality of membrane components areformed of a non-porous material.